This is only applicable to vehicles which have manual systems of heating and air conditioning since those with automatic systems are intricate and have to be sent to a reputable service center. The first step is to verify that the battery is completely charged by checking the fuses and all connections in the circuit are loose and free of corrosion. Put the transaxle in Park or Neutral and firmly install the parking brake. Take out the glove box and put the ignition switch to the Run position without starting the vehicle. Using a back probe, energize the electrical connector of the blower motor and a voltmeter to the two terminals. Test the blower switch in each of the positions and record the voltage values because they change with variation in the speed of the motor. In case there is voltage and the blower motor is not operating, verify the continuity of the ground wire between the motor and the chassis. When the ground wire is thin, then the blower motor is probably defective; disconnect the motor connector and check it by connecting one end to a chassis ground and by connecting the other end to a fused battery voltage source. When the blower fails to work, then it is defective. Assuming that there was a zero voltage on the blower motor at one or more of the speeds and that the motor checked is good, examine blower motor resistor. Unattach the electric connector to the resistor and, with the ignition On, test each terminal with the blower switch to the speed positioning. When the voltmeter is not functioning properly, and the blower is known to be working, then the resistor is probably faulty; no voltage at the switch, then the switch or control panel and the wiring may be the problem.